The invention relates to the preparation of ether ketones and ether aldehydes. In particular, the invention relates to a catalytic dehydrogenation of alkylene glycol ethers to produce ether ketones and ether aldehydes.
Primary alcohols can be converted to aldehydes and secondary alcohols to ketones by dehydrogenation. Similarly, glycol ethers can be converted to ether aldehydes or ether ketones. Catalytic dehydrogenation is more often used industrially because it gives relatively high selectivity to aldehydes or ketones.
U.S. Pat. No. 3,462,495 teaches dehydrogenation of glycol ethers with xe2x80x9ccalcium nickel phosphatexe2x80x9d catalysts. The dehydrogenation is performed by feeding a mixture of glycol ether with from 1 to 25% of water at 425xc2x0 C. It gives 55% of conversion of glycol ether and 72.5% selectivity to ether ketone.
U.S. Pat. No. 4,233,246 teaches oxidation of glycol ethers to ether ketones with silver/copper metal catalysts in the presence of air. The reaction is carried out in vapor phase by passing glycol ether through multiple layers of catalyst at 450-700xc2x0 C. While this complicated process gives a high conversion of glycol ether ( greater than 99%), it has low selectivity to ether ketone (less than 70%).
U.S. Pat. No. 4,141,919 teaches dehydrogenation of propylene glycol methyl ether in the presence of copper oxide catalyst. The catalyst is treated with hydrogen. A mixture of propylene glycol methyl ether with about 5% of water is passed over the catalyst at about 280xc2x0 C. It gives less than 50% selectivity to methoxyacetone.
U.S. Pat. No. 4,431,493 teaches electrochemical preparation of ether ketones and ether aldehydes from alkylene glycol ethers. However, the conversion and selectivity are still very low.
A Czech and Slovak patent, C.S. Pat. No. 275,182, also teaches dehydrogenation of propylene glycol methyl ether to methoxyacetone with copper-zinc oxides. The patent discloses that using an aniline derivative in the dehydrogenation can enhance the selectivity to methoxyacetone.
Copending appl. Ser. No. 09/519,398, filed on Mar. 3, 2000, discloses liquid phase oxidation of propylene glycol methyl ether to methoxyacetone using hydrogen peroxide in the presence of a transition metal catalyst. It has achieved a higher conversion and higher selectivity. However, using hydrogen peroxide is inconvenient in a commercial process.
There is an increasing interest in ketones and aldehydes. They are used for making dyes and herbicidal compositions (see, e.g., U.S. Pat. Nos. 4,666,502 and 5,576,188). Ether ketones have found potential uses as co-solvents in water-borne coatings (see, e.g., U.S. Pat. No. 4,202,808). An improved process for making ether ketones and ether aldehydes is thus needed. Ideally, the process would have high selectivity and could be easily commercialized.
The invention is a process for dehydrogenation of an alkylene glycol ether to an ether ketone or an aldehyde. The process is performed in the presence of a copper chromite catalyst and at least 5 wt % of water based on the amount of alkylene glycol ether. The process gives high selectivity to ketones and aldehydes.
The invention is a process for dehydrogenation of alkylene glycol ethers to ether ketones and aldehydes. The process is performed in the presence of a copper chromite catalyst. Suitable copper chromite catalysts can be made by any method known in the art. For example, U.S. Pat No. 3,374,184, the teachings of which are incorporated herein by reference, teaches making copper chromite by reacting cupric nitrate and chromic oxide. In another example, U.S. Pat, No. 4,251,396, the teaching of which are incorporated herein by reference, teaches making copper chromite from copper sulfate and sodium dichromate. Copper chromite catalysts are commercially available, e.g., from Engehard Company. Preferably, the copper chromite for use in the process of the invention contains at least 50 wt % of CuCr2O4.
The catalyst is preferably treated with hydrogen. Methods for hydrogenation of metal oxides are known. For example, U.S. Pat. No. 4,141,919, the teachings of which are incorporated herein by reference, teaches how to hydrogenate copper oxide. The hydrogenation of copper chromite is exothermic, so hydrogen is added slowly in the beginning and gradually increased when the reaction continues. The hydrogenation is preferably carried out at a temperature from about 125xc2x0 C. to about 225xc2x0 C., more preferably from about 150xc2x0 C. to about 200xc2x0 C.
The catalyst preferably has a total pore volume within the range of about 0.05 to about 2 cc/g, more preferably from 0.05 to 0.5 cc/g. It preferably has a surface area within the range from about 1 to about 50 m2/g, more preferably from about 5 to about 15 m2/g.
The process of the invention is performed in the presence of at least 5 wt % of water based on alkylene glycol ether. Preferably, the dehydrogenation is performed in the presence of at least 20 wt % of water. More preferably, the process is performed in the presence of at least 40 wt % of water. As shown in the examples, the selectivity to ether ketones increases with increasing water concentration. When about 40 wt % of water is used, the selectivity reaches almost 100%.
Suitable alkylene glycol ethers for use in the dehydrogenation include those having the general structure: 
in which R1 is a C1 to C10 alkyl group, or a C6 to C10 aryl or alkylaryl group, R2 is hydrogen, a C1 to C10 alkyl group, or a C6 to C10 aryl or alkylaryl group, and n, which is an average number of oxyalkylene units, is within the range of 1 to about 10. Preferably, n is within the range of 1 to about 5. More preferably, n is within the range of 1 to about 3. Preferably, R1 is a C1 to C10 alkyl group. More preferably, R1 is a C1 to C6 alkyl group. Preferably, R2 is hydrogen or a C1 to C10 alkyl group. More preferably, R2 is hydrogen or methyl group.
Examples of suitable alkylene glycol ethers are propylene glycol methyl ether, propylene glycol n-butyl ether, propylene glycol t-butyl ether, propylene glycol n-propyl ether, dipropylene glycol methyl ether, dipropylene glycol n-butyl ether, dipropylene glycol t-butyl ether, dipropylene glycol n-propyl ether, tripropylene glycol methyl ether, ethylene glycol methyl ether, ethylene glycol n-butyl ether, diethylene glycol methyl ether, diethylene glycol n-propyl ether, and the like, and mixtures thereof.
The dehydrogenation converts primary hydroxyl group of alkylene glycol ether to aldehyde and secondary hydroxyl group to ketone. For example, dehydrogenation of propylene glycol methyl ether gives methoxyacetone, while the dehydrogenation of ethylene glycol methyl ether gives methoxyformaldehyde. Ether ketones and aldehydes prepared by the hydrogenation of the invention include those represented by the formula: 
R1, R2 and n are defined above.
The process is preferably performed at a temperature within the range of about 150xc2x0 C. to about 350xc2x0 C. More preferably, the process is performed at a temperature within the range of about 220xc2x0 C. to about 280xc2x0 C.